1. Field of the Invention
The present invention discloses a stereoscopic display device, more particularly, a stereoscopic display device that can be switched freely between 2D/3D display modes.
2. Description of the Prior Art
In recent years, many stereoscopic display modes have been developed to make observers obtain stereoscopic images. A so-called stereoscopic image is produced by providing separated images to each eye respectively. The brain therefore analyzes the overlapping images and calculates the depth and gradation of each component to make the observer obtain a stereoscopic image. Hence, a stereoscopic device is a means to present different images to the left eye and the right eye individually so that the observer can sense a stereoscopic image. As shown in FIG. 1, the images for the left eye L and the right eye R are separated by the parallax barrier 1 and captured by the observer to produce a stereoscopic image.
In general, stereoscopic display devices can be classified into passive stereoscopic display devices and auto stereoscopic display devices. For passive stereoscopic display devices, the user should wear some assisting equipment, for example, polarization glasses. For auto stereoscopic display devices, the observer does not need to wear assisting equipment. The auto stereoscopic display devices can use a double convex lens, a lens array, or a parallax barrier to separate the images for the left eye and the right eye to produce a stereoscopic image, among which, the parallax barrier is the most widely used.
A parallax barrier comprises a grating structure to separate the information of each eye. In general, the parallax barrier can be a simple grating structure made by plastics or metals like chromium, or be an LCD panel. Using an LCD panel as a parallax barrier can not only produce a 3D stereoscopic image. It also can be switched between 2D/3D modes freely by controlling the power. Please refer to FIG. 2, showing a schematic diagram illustrating a conventional stereoscopic display device using an LCD panel as the parallax barrier. The stereoscopic display device 2 comprises a display unit 21 and a parallax barrier 22. The display unit 21 can display images and generally is an LCD panel. The parallax barrier 22 comprises two substrates 221, 222 and two layers of ITO electrodes 223, 224 that are disposed on the two substrates 221, 222. The electrode 223 comprises a grating structure and the electrode 224 comprises a plane structure. A liquid crystal layer 225 is formed by injection liquid crystal molecular between the two electrodes 223, 224. When operating the 3D mode, a driving voltage is applied to the electrodes 223, 224 and the parallax barrier 22 forms a grating pattern that is bright-dark interlacing, therefore, the observer can obtain a stereoscopic image. On the other hand, when operating the 2D mode, no driving voltage is applied to the electrodes 223, 224, and the observer therefore obtains a flat 2D image. However, when under the 3D mode, at least half image of the display unit 21 is blocked by the grating pattern, thereby reducing half of the brightness and the resolution of the stereoscopic display device 2.
In order to solve this problem, a time-sharing type barrier is developed, as shown in FIGS. 3a and 3b. Compared to conventional arts, the electrodes 223 are divided into two groups, an odd electrode group 3231 and an even electrode group 3232. During the first period, a driving voltage is only applied to the odd electrode group 3231 and a grating pattern is formed; next during the second period, the driving voltage is switched to the even electrode group 3232 and the image for each eye is exchanged at the same time. As a result, the observer can obtain a 3D stereoscopic image in the same resolution as in the 2D mode when operating the first period and the second period periodically.
However, when the parallax barrier is in a normally white mode of transmission, only the portion of the charged electrode group turns to black. Whether in the first or second period, the opening aperture d in FIG. 3a is so large that the aperture ration exceeds up to 50%, causing serious cross-talk interruption between two eyes. Regarding this problem, EP1793623 discloses a stereoscopic display device that comprises an LCD panel in a normally black mode of transmission so that only the portions of charged electrodes turn to white and other portions remain black. The opening aperture e in FIG. 3a is small, keeping the lower aperture ratio and a better display quality. However in EP1793623, a normally black mode LCD is used as the parallax barrier, it can not be switched between 2D/3D modes and thereby causes poor utilization.
Accordingly, a parallax barrier that can be switched between 2D/3D modes and comprises a low opening aperture is still needed in the industry.